Fully agree with imj. Being someone who can wait awhile rather than queue all night for a phone just because it's got a higher number in its title, I always buy my chosen phone outright when I spot a deal at the right price. I daresay there are potential drawbacks but I've not met one yet.
...........and make sure that the warranty for the device is valid in the UK.
Absolutely, AQ. Don't buy from eBay unless it's a bona fide UK outlet.